This invention relates to fire extinguishant bottle mechanisms of the type shown for example in U.S. Pat. No. 3,209,937 issued to R. Hirst et al. or U.S. Pat. No. 3,915,237 issued to E. Rozniecki. Such mechanisms commonly comprise upright bottles charged with a pressurized liquid fire extinguishant material such as CF.sub.3 Br (brand name Halon 1301); the pressurizing agent is commonly nitrogen, and the charging pressure is usually sufficient to bring the bottle pressure up to about 750 p.s.i. In the absence of the pressurizing agent the fire extinguishant material would have a vapor pressure of about 229 p.s.i.a. at 75.degree. F. An automatic valve is located at the lower end of the bottle to discharge the pressurized extinguishant toward the developing fireball.
In one particular system, developed for use in military vehicles to combat explosive fires generated by enemy bullets fired through the vehicle fuel tank, the automatic valve is triggered to the valve-open condition by means of an optical sensor responsive to radiations produced by the developing fireball. The electrical signal generated by the activated sensor is amplified and directed through a hot wire filament contained within a small explosive squib suitably mounted on the valve. As the squib explodes high pressure gases (about 3000-4000 p.s.i.) are generated behind a piston-like cutter element aligned with a diaphragm that seals the liquid extinguishant within the charged bottle; the cutter element severs the diaphragm from the valve body (partially or wholly) to enable the pressurized extinguishant to flow rapidly through the valve toward the developing fireball. In a preferred arrangement the entire process from initial activation of the sensor to extinguishment of the fireball takes place in 100 milliseconds or less.
In military vehicles the space available for the bottle-valve assembly is somewhat restricted. It is therefore desirable that the valve occupy minimum space below the bottle. Another desirable feature is the inclusion of a back-up actuator for the valve in the event that the explosive squib fails to fire. The present invention is directed to a valve structure having these desired features, namely small space requirement and back-up actuation means. In a preferred arrangement the valve is designed for relatively low cost manufacture, using relatively few component parts. The valve element is a poppet valve rather than the commonly-used rupturable diaphragm; therefore the valve assembly can be reused (after each fire-extinguishant activity) without need for valve element replacement. Preferred poppet valve resembles the intake-exhaust valves commonly used in internal combustion engines for withstanding high combustion chamber pressures.
In systems using Halon 1301 it is necessary that the pressurizing agent (nitrogen) be intimately mixed with the liquid extinguishant when the agent is first introduced to the bottle; such mixing promotes rapid dissolving of the agent in the Halon. If the pressurizing agent and Halon do not go into solution during the charging period then slow dissolving of the agent after completion of the charging operation will result in a lowered bottle pressure and consequent slow Halon released toward the fireball when the valve is opened. Intimate mixture of the pressurizing agent and the Halon during the initial charging operation may be achieved by agitation of the bottle and/or slow bubbling of the agent from the bottom of the bottle upwardly through the extinguishant liquid. Conventional practice is to charge the bottle through a small bypass opening in the aforementioned diaphragm valve. Our valve design is not especially suited to the incorporation of a bypass opening for charge-in action. Therefore we provide a separate charge-in fitting at the top of the bottle; a filler tube extends from this fitting downwardly into the bottle to introduce the pressurizing agent into the bottle at a point below the surface of the liquid extinguishant. The agent is permitted to slowly bubble upwardly through the liquid, thereby assisting the agent to go into solution.
The separate charge-in fitting at the top of the bottle advantageously incorporates a safety rupture disc and pressure gage. In conventional arrangements where the bottom valve is used for charging purposes it is not always possible to incorporate a pressure gage and/or safety disc without unduly complicating the valve, increasing its manufacturing cost, or appreciably increasing its bulk. Our arrangement provides a combination of features not always available in comparable prior art arrangements. Use of a separate charge-in valve at the upper end of the bottle is compatible with high flow rate, rapid response discharge valve at the lower end of the bottle.